1. Field of the Invention
This invention relates to a webbing-locking mechanism suitable for use in a vehicle seat belt.
2. Description of the Prior Art
In order to protect a vehicle occupant from a secondary collision against interior structural members or parts of the vehicle or a similar hazard in case of emergency such as collision or the like accident, it has become necessary to minimize the length of a webbing which may be paid out from its retractor upon such an emergency.
The above consideration is particularly important for an automatic seat belt which restrains a vehicle occupant automatically when he has sat on the seat and closed the door, because more webbing is taken up in the retractor and the webbing may be paid out over a considerable length due to the tightening of the webbing wound on a take-up reel in case of emergency, thereby failing to effectively protect the vehicle occupant. With a view toward solving such a problem, a variety of locking devices or mechanisms have been proposed to lock each webbing between its corresponding retractor and a point where the webbing is first brought into contact with the vehicle occupant. Many of such locking devices or mechanisms are of such a type that a guide roller is provided to allow a webbing to extend over a predetermined length of its circumference and the webbing is held between the guide roller and its matching clamp member. It has also been known that, in a webbing-locking device or mechanism of such a type as mentioned above, the webbing may be locked more effectively by stopping rotation of the guide roller so as to make use of a friction resistance to be developed between the thus-stopped guide roller and the webbing.
As one way of stopping the rotation of a guide roller, it has conventionally been known to use such a mechanism as shown in FIG. 1. Namely, when the tensile force applied to a webbing W wrapped over a guide roller 1 exceeds a predetermined value, the guide roller 1 turns clockwise together with a lever 2 about a pin 3 and the webbing W is thus held between the guide roller 1 and a clamp plate 4. Here, a locking member 5, which serves to stop the rotation of the guide roller 1, moves together with the lever 2, thereby bringing a guide member 6 provided integrally with the locking member 5 into contact with a guide pin 7 and thus turning the locking member 5 counterclockwise. The locking member 5 is therefore brought into engagement with the guide roller 1 so as to stop the rotation of the guide roller 1. Owing to the spring force of a return spring 8 provided with the locking member 5, the locking member 5 and guide roller 1 are disengaged from each other when the tensile force has been released.
In the above-referred to locking mechanism, it is indispensable to incorporate the return spring 8 for allowing the locking member 5 to assume its normal position. This renders the structure unavoidably complex in the vicinity of the locking member 5, thereby raising such problems that parts or members interfere with one another and their assembly work takes lots of time.